Microfabricated micro fluid channels

ABSTRACT

A fluid delivery system including a first substrate having a micro-channel and a well both formed through the first substrate. The fluid delivery system also includes a second substrate and a delivery channel. The second substrate is on the first substrate and the delivery channel is formed between the first and second substrates. The delivery channel provides fluid communication between the micro-channel and the well.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] The subject matter of this application may in part have beenfunded by National Science Foundation and DARPA/AFOSR. The governmentmay have certain rights in this invention.

BACKGROUND

[0002] This invention relates generally to array chemical transferdevices, and in particular, to a fluid delivery system having an arrayof micro-channels in fluid connection with an array of wells.

[0003] In nanolithography, such as dip pen lithography (DPN) or othertypes of arrayed chemical transfer methods, it is desirable to provideinks, chemical or biological fluids, to a plurality of probessimultaneously. An arrayed fluid dispensing system with matching spatialconfiguration to the probe array would allow efficient inking of such anarray of probes. Neighboring probes with very small distances betweenthem can receive distinct inks. The probes can then be used to createhigh density arrays of biochemical substances, such as, DNA or proteinarrays.

BRIEF SUMMARY

[0004] According to one aspect of the present invention, a method forfabricating a fluid delivery system is provided. The method includesattaching a first substrate and a second substrate to form a deliverychannel between the first substrate and the second substrate. Thedelivery channel provides fluid communication between a firstmicro-channel and a first well. The first micro-channel and the firstwell are both in the first substrate.

[0005] According to another aspect of the present invention, a fluiddelivery system is provided. The fluid delivery system includes a firstsubstrate having a micro-channel and a well both formed through thefirst substrate. The fluid delivery system also includes a secondsubstrate and a delivery channel. The second substrate is on the firstsubstrate and the delivery channel is formed between the first andsecond substrates. The delivery channel provides fluid communicationbetween the micro-channel and the well.

[0006] According to another aspect of the present invention, a methodfor forming a micro-pipette is provided. The method includes etching atop surface of a substrate to remove a portion of the substrate. Thesubstrate has a micro-channel formed through the first substrate, wherethe top surface is opposed to a bottom surface. The top surface, thebottom surface, and the micro-channel, are coated with a supportmaterial.

[0007] According to another aspect of the present invention, anapparatus for transferring fluid is provided. The apparatus includes asubstrate having a top surface opposed to a bottom surface and a layerof support material. The substrate and the layer of support materialform a micro-channel. The micro-channel opens at the bottom surface ofthe substrate and extends above the top surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 illustrates a cross-sectional view of a fluid deliverysystem containing multiple substrates, in accordance with one preferredembodiment of the invention;

[0009]FIG. 2 illustrates a cross-sectional view of a fluid deliverysystem containing multiple substrates, in accordance with one preferredembodiment of the invention;

[0010]FIG. 3. illustrates an enlarged cross-sectional view of a portionof a fluid delivery system containing multiple substrates, in accordancewith one preferred embodiment of the invention;

[0011]FIG. 4. illustrates a cross-sectional view of a fluid deliverysystem containing multiple substrates, in accordance with one preferredembodiment of the invention;

[0012]FIG. 5. illustrates a cross-sectional view of a fluid deliverysystem containing multiple substrates, in accordance with one preferredembodiment of the invention; and

[0013]FIGS. 6-11 illustrate, in cross-section, process steps for thefabrication of a micro-pipette structure for use in a fluid deliverysystem in accordance with one preferred embodiment of the invention.

[0014] It should be appreciated that for simplicity and clarity ofillustration, elements shown in the Figures have not necessarily beendrawn to scale. For example, the dimensions of some of the elements areexaggerated relative to each other for clarity. Further, whereconsidered appropriate, reference numerals have been repeated among theFigures to indicate corresponding elements.

DETAILED DESCRIPTION

[0015] The present invention includes micro fluid channels. The microfluid channels are formed by etching partially or completely through asubstrate. The micro fluid channels may protrude from the substrate toform micro-pipettes, which may be in the form of an array. The channelsmay be part of a fluid delivery system, including one or more additionalsubstrates, with channels between the substrates connecting the microfluid channel to wells having a larger size, allowing for various fluidsto easily be delivered to the micro fluid channel. These micro fluidchannels may then be used to ink a probe or array of probes, to spotsurfaces. This will allow for patterning, with the various fluids, toform, for example high density arrays of biochemical substances.

[0016] A “micro fluid channel” or “micro-channel” means a channel havinga cross-sectional area of at most 10,000 square microns, more preferablyat most 2500 square microns, most preferably at most 100 square microns.

[0017] Shown in FIG. 1, in cross-section, is a fluid delivery system 20which includes a first substrate 28 overlying a second substrate 54.Preferably, the first and second substrate 28, 54 comprises a singlecrystal silicon substrate, however, first and second substrate 28, 54may comprise other materials. Preferably, the substrate 28, 54 each havea thickness of 1000 to 200 microns, such as 300 to 500 microns.Preferably, the first and second substrates 28, 54 have top surfaces 30,56 which are previously processed and cleaned to remove debris andnative oxides.

[0018] First substrate 28 has a top surface 30 opposed to a bottomsurface 32. First substrate 28 also has an outer edge 24 surrounding aninside surface 26, as illustrated in FIG. 1. In one embodiment, thefirst substrate 28 is formed from a single substrate, as illustrated inFIGS. 1 and 4, while in another embodiment, the first substrate 28 isformed from multiple substrates, such as an upper substrate 50 and alower substrate 52, and then bonded together, as illustrated in FIGS. 2and 5.

[0019] Upper and lower substrates 50, 52 may be bonded in one of manyways, such as spin on bonding using photoresist or an adhesive polymerfor adhesive bonding, which may be patterned (see for example “VOID-FREEFULL WAFER ADHESIVE BONDING” F. Niklaus, et al.); or high-temperaturebonding, for example by heating the substrates together at about 1100°C. Alignment may be achieved using alignment mark, or using featurespresent on the substrates.

[0020] A micro-channel 34 is formed through the first substrate 28 fromthe top surface 30 to the bottom surface 32. Preferably, themicro-channel 34 is formed by etching all the way through the firstsubstrate 28 from the top surface 30 to the bottom surface 32, howeverother means for forming the micro-channel 34 may be used, such asdrilling. Preferably, the micro-channel 34 is formed using anisotropicetching. In one embodiment, the micro-channel 34 is formed by etchingthrough the top surface 32 to formed a first channel 40 and then etchingthrough the bottom surface 32 to form a second channel 42, wherein thefirst and second channels 40, 42 are in fluid communication, asillustrated in FIG. 7. Preferably, the cross-sectional area of the firstchannel 40 is less than the cross-sectional area of the second channel42. More preferably, the ratio of the cross-sectional area of the firstchannel 40 to the cross-sectional area of the second channel 42 isbetween 1 to 1 and 1 to 10.

[0021] The micro-channel 34 has an inlet 38 for receiving fluid 22 froma delivery channel 66 and an outlet 36 for delivering fluid 22,preferably, to a probe 78, as illustrated in FIG. 3. In one embodiment,the outlet 36 has a cross-sectional area that is generally circular inshape. Preferably, the outlet 36 has a cross sectional area that is atmost 10,000 square microns, more preferably at most 2,500 squaremicrons, and most preferably at most 100 square microns. In oneembodiment, the outlet 36 has a cross sectional area that is between tenand 10,000 square microns. Preferably, the inlet 38 has across-sectional area that is larger than the cross-sectional area of theoutlet 36. The cross-sectional areas and shapes of the inlet 38 and theoutlet 36 may be freely chose, using patterning techniques, such asthose used to pattern semiconductor substrates.

[0022] Preferably, the first substrate 28 includes a hydrophobic surface74 surrounding the outlet 36, as illustrated in FIG. 1. The hydrophobicsurface 74 prevents fluid 22 from overflowing and unintentionallyexiting the outlet 36, and possibly causing cross-contamination betweenfluids 22. The hydrophobic surface 74 can be formed in one of many ways,such as, coating the outlet 36 of the micro-channel 34 with ahydrophobic material, for example a silane or thiol, such as1-octadecanethio (ODT), or a photoresist. Preferably, an array ofmicro-channels 34 are formed through the first substrate 28 from the topsurface 30 to the bottom surface 32, as illustrated in FIG. 1. Thedistance D₁ between adjacent micro-channels 34 is preferably at most1000 microns, more preferably at most 600 microns, most preferably atmost 200 microns.

[0023] A well 44 is formed through the first substrate 28 from the topsurface 30 to the bottom surface 32. Preferably, the well 44 is formedby etching all the way through the first substrate 28 from the topsurface 30 to the bottom surface 32, however other means for forming thewell 44 may be used, such as, drilling. Preferably, the well 44 isformed using reactive ion etching. The well 44 has an inlet 46 forreceiving fluid 22 from a fluid delivery device, such as, a conventionalpipette or pump. The well 44 also includes an outlet 36 for deliveringfluid 22 to the delivery channel 66, as illustrated in FIG. 1. In oneembodiment, the inlet 46 has a cross-sectional area that is generallycircular is shape. Preferably, the inlet 46 has a cross-sectional areathat is greater than the cross-sectional area of the outlet 36. Formingan inlet 46 with a cross-sectional area that is larger than thecross-sectional area of the outlet 36 allows for fluids 22 to be easilyinjected into the inlet 46, and yet still be deliverable, through thesmaller outlet 36, to a probe 78. Preferably, the inlet 46 has a crosssectional area that is between 1 and 20 square millimeters, morepreferable between 3 and 12 square millimeters, and most preferably,between 5 and 10 square millimeters. In one embodiment, the distance D₃between adjacent wells 44 is greater than the distance D₁ betweenadjacent micro-channels 34 or the distance D₂ between adjacentmicro-pipettes 84, as illustrated in FIGS. 1 and 2.

[0024] Preferably, an array of wells 34 are formed through the firstsubstrate 28 from the top surface 30 to the bottom surface 32, asillustrated in FIG. 1. Preferably, the array of wells 34 are formed nearthe outer edge 24 of the first substrate 28, while the array ofmicro-channels 34 are formed at the inside surface 26 of the firstsubstrate 28, as illustrated in FIG. 1.

[0025] Second substrate 54 has a top surface 56 opposed to a bottomsurface 58. Second substrate 54 also has an outer edge 62 surrounding aninside surface 64, as illustrated in FIG. 1. Second substrate 54 ispositioned so that the top surface 56 is on the bottom surface 32 of thefirst substrate 28. In one embodiment, an extended channel 60 is formedthrough the second substrate 54 from the top surface 56 to the bottomsurface 58. Preferably, the extended channel 60 is formed by etching allthe way through the second substrate 54 from the top surface 56 to thebottom surface 58, however other means for forming the extended channel60 may be used, such as, drilling. Preferably, the extended channel 60is formed using reactive ion etching. The extended channel 60 has aninlet 61 for receiving fluid 22 from a secondary delivery channel 67 andan outlet 63 for delivering fluid 22 to the inlet 38 of themicro-channel 34, as illustrated in FIGS. 1 and 3. In one embodiment,the outlet 63 has a cross-sectional area that is generally circular isshape.

[0026] A delivery channel 66 is formed between the first and secondsubstrates 28, 54, as illustrated in FIGS. 1 and 2. Preferably, theheight H of the delivery channel, as illustrated in FIG. 3, is betweenone and twenty microns, and more preferably, at most ten microns. Thedelivery channel 66 may be formed in one of many ways. In oneembodiment, the delivery channel 66 includes a groove that is formed onthe top surface 56 of the second substrate 54. In one embodiment, thedelivery channel 66 includes a groove that is formed on the bottomsurface 32 of the first substrate 28. In one embodiment, the deliverychannel 66 includes a first groove that is formed on the top surface 56of the second substrate 54 and a second groove that is formed on thebottom surface 32 of the first substrate 28. The first substrate 28 isaligned with the second substrate 54 so that the delivery channel 66allows for fluid to travel between the micro-channel 34 and the well 44.The delivery channel 66 includes an inlet 70 for receiving fluid and anoutlet 68 for delivering fluid 22. The inlet 70 receives fluid 22 fromthe outlet 48 of the well 44, while the outlet 68 delivers fluid 22 tothe inlet 38 of the micro-channel 34. The inlet 70 is adjacent to theoutlet 48 and the outlet 68 is adjacent to the inlet 38, as illustratedin FIG. 1.

[0027] In one embodiment, the micro-channel 34 extends both above andbelow the top surface 30 of the first substrate 28, as illustrated inFIGS. 2-5. In this embodiment, the micro-channel 34 may be formedentirely from the first substrate 28, a portion of the micro-channel 34may be formed from the first substrate 28, or the micro-channel 34 beformed from a second material. The second material may be any materialthat can be formed or coated onto a surface, such as those used insemiconductor processing. Examples include oxides, such as silicon oxideand silicon oxynitride, nitrides such as silicon nitride and titaniumnitride, metals such as tungsten and gold, and polymers. Preferably, themicro-channel 34 is formed from the second material, wherein the secondmaterial extends both above and below the top surface 30 of the firstsubstrate 28.

[0028] In one embodiment, a method for fabricating the fluid deliverysystem 20 is disclosed. Referring to FIG. 1 the fluid delivery system 20is fabricated by attaching the first substrate 28 and the secondsubstrate 54 to form the delivery channel 66, wherein the deliverychannel 66 provides fluid communication between the micro-channel 34 andthe well 44. Preferably, the first substrate 28 is aligned with thesecond substrate 54 so that the inlet 70 of the delivery channel 66 isadjacent the outlet 48 of the well 44, while the outlet 68 of thedelivery channel 66 is adjacent the inlet 38 of the micro-channel 34. Inthis way, the micro-channel 34 is in fluid connection with the well 44and thus fluid 22 may travel from the inlet 46 of the well 44 throughthe well 44, the delivery channel 66, and the micro-channel 34, only toexit at the outlet 36 of the micro-channel 34. Preferably, eitheralignment marks or existing features on either at least one or both thefirst and second substrates 28, 54 are used to align the first substrate28 with the second substrate 54.

[0029] Once the delivery channel 66 is formed, the fluid 22 is deliveredto the well 44. The fluid 22 travels down the well 44, through thedelivery channel 66, and up the micro-channel 34 to the outlet 36. Fluid22 can be forced up into the micro-channel 34 by pumping the fluid 22through the well 44 and the delivery channel 66. Fluid 22 may be pumpedthrough the well 44 and the delivery channel 66 using a variety oftechniques, such as, by creating a pressure differential between theinlet 46 and the outlet 36, or simply by capillary action. Preferably,the fluid 22 is kept in the micro-channel 34 and prevented fromunintentionally exiting the micro-channel 34 by creating a hydrophobicsurface 74 adjacent the outlet 36 of the micro-channel 34. Once themicro-channel 34 is filled with fluid 22, the fluid 22 can then betransferred to a probe 78, such as an SPM (Scanning Probe Microscopy)probe, and more specifically to the tip 80 of the probe 78, asillustrated in FIG. 3.

[0030] In one embodiment, a micro-pipette 84 forms the micro-channel 34.Preferably, a portion of the micro-pipette 84 extends both above andbelow the top surface 30 of the first substrate 28, as illustrated inFIG. 2. Preferably, the fluid delivery system 20 includes an array ofmicro-pipettes 84, as illustrated in FIGS. 2-5, allowing for multiplefluids 22 to be dispensed from the an array of micro-channels 34.

[0031] In one embodiment, a method for fabricating the micro-pipette 84is disclosed, as illustrated in FIGS. 6-11. Referring to FIG. 6, asubstrate 88, such as first substrate 28, is provided. Preferably, thesubstrate 88 has a top surface 90 which is previously processed andcleaned to remove debris and native oxides. The top surface 90 isopposed to a bottom surface 92. Preferably, the bottom surface 92 isalso previously processed and cleaned to remove debris and nativeoxides.

[0032] Referring to FIG. 7, a channel 94, such as a micro-channel 34,having a wall 95 is formed through the substrate 88 from the top surface90 to the bottom surface 92. Preferably, the channel 94 is formed byetching all the way through the substrate 88 from the top surface 90 tothe bottom surface 92, however other means for forming the channel 94may be used, such as drilling. Preferably, the channel 94 is formedusing reactive ion etching. In one embodiment, the channel 94 is formedby etching through the top surface 92 to form a first channel 100 andthen etching through the bottom surface 92 to form a second channel 102,wherein the first and second channels 100, 102 connect, as illustratedin FIG. 7. The channel 94 has an inlet 98 for receiving fluid, such asfluid 22, and an outlet 96 for delivering fluid to, for example, aprobe, such as probe 78. In one embodiment, the outlet 96 has across-sectional area that is generally circular is shape. In yet anotherembodiment, the inlet 98 has a cross-sectional area that is larger thanthe cross-sectional area of the outlet 96. The cross-sectional areas andshapes of the inlet 98 and the outlet 96 may be freely chose, usingpatterning techniques, such as those used to pattern semiconductorsubstrates.

[0033] After forming the channel 94, the top surface 90, the bottomsurface 92, and the wall 95 of the channel 94 are all coated with alayer 76 of support material, as illustrated in FIG. 8. The supportmaterial may include any material that can be formed or coated onto asurface, such as those used in semiconductor processing. Examplesinclude oxides, such as silicon oxide and silicon oxynitride, nitridessuch as silicon nitride and titanium nitride, metals such as tungstenand gold, and polymers. The support material may be formed by chemicalreaction with the substrate 88, for example by oxidation, or by coating,for example with chemical vapor deposition or oblique angle physicalvapor deposition. Preferably, the support material is different from thematerial contained in the substrate 88. Multiple materials may also beused; these may be applied with the first support material, or they maybe applied after further processing steps. In one embodiment, the layer76 is silicon dioxide which is formed by reacting the substrate 90,preferably made of silicon, with oxygen.

[0034] After forming the layer 76, a portion of the layer 76 is removed.Preferably, the layer 76 is removed from the top surface 90 to exposethe top surface 90 of the substrate 88. In one embodiment, the layer 76is removed from the bottom surface 92 to expose the bottom surface 92 ofthe substrate 88. Layer 76 may be removed in on of a number of ways,such as the use of chemical-mechanical polishing or etching. The channel94 may be filled with a protectant, such as wax, to avoid damaging thechannel 94 with a polishing agent. The protectant may be removed with asolvent, such as acetone.

[0035] Upon removing the layer 76, the substrate 88 is then etched toremove a portion of the either the top surface 90 or the bottom surface92 of the substrate 88, as illustrated in FIG. 10. Preferably, thesubstrate 88 is etched to a depth D₄, as illustrated in FIG. 10, ofbetween 50 and 500 microns, and more preferably, a depth of at most 150microns. Various types of etching may be used to remove a portion of thesubstrate 88, such as wet etching with ethylene diamine pyrocatechol orpotassium hydroxide, or dry etching. Preferably, the top surface 90 isetched to remove a portion of the substrate 88 and create an etchedsurface 91 which is closer to the bottom surface 92 than the originaltop surface 90.

[0036] Preferably, upon etching the substrate 88, a hydrophobic materialis applied to the surface 106 surrounding the outlet 96 to create ahydrophobic surface 108, as illustrated in FIG. 11.

[0037] The individual processing steps used in accordance with thepresent invention are well known to those of ordinary skill in the art,and are also described in numerous publications and treatises,including: Encyclopedia of Chemical Technology, Volume 14 (Kirk-Othmer,1995, pp. 677-709); Semiconductor Device Fundamentals by Robert F.Pierret (Addison-Wesley, 1996); Silicon Processing for the VLSI Era byWolf (Lattice Press, 1986, 1990, 1995, vols 1-3, respectively); andMicrochip Fabrication: A Practical Guide to Semiconductor Processing byPeter Van Zant (4^(th) Edition, McGraw-Hill, 2000). In order to etchthrough the substrate, techniques such as deep ion etching may be used(also known as the Bosch process).

[0038] The fluid delivery system may be used to form patterns usingfluids on surfaces. For example, if the fluid is an ink, then a surface,such as paper could be printed with the probes after they have receivedthe ink, to form microprinting. Biological arrays may similarly beformed, for example by using fluids containing biological compounds,such as nucleotides (RNA, DNA, or PNA), proteins (enzymes, antibodies,etc.), lipids, carbohydrates, etc. to spot a substrate, such as glass,silicon, or polymers. Since each micro-channel may be supplied for adedicated well, very complex arrays may be produced quickly.

[0039] Numerous additional variations in the presently preferredembodiments illustrated herein will be determined by one of ordinaryskill in the art, and remain within the scope of the appended claims andtheir equivalents. For example, while the examples provided above relateto silicon-based semiconductor substrates, it is contemplated thatalternative semiconductor materials can likewise be employed inaccordance with the present invention, and that the semiconductorsubstrates may be undoped, P-doped, or N-doped. Suitable materials forthe substrates include but are not limited to silicon, gallium arsenide,germanium, gallium nitride, aluminum phosphide, Si_(l−x)Ge_(x) andAl_(x)Ga_(l−x)As alloys, wherein x is greater than or equal to zero andless than or equal to one, the like, and combinations thereof.Additional examples of materials for use in accordance with the presentinvention are set forth in Semiconductor Device Fundamentals by RobertF. Pierret (p. 4, Table 1.1, Addison-Wesley, 1996).

[0040] Although the invention has been described and illustrated withreference to specific illustrative embodiments thereof, it is notintended that the invention be limited to those illustrativeembodiments. Those skilled in the art will recognize that variations andmodifications can be made without departing from the spirit of theinvention.

1. A method for fabricating a fluid delivery system, comprising:attaching a first substrate and a second substrate to form a deliverychannel between the first substrate and the second substrate, whereinthe delivery channel provides fluid communication between a firstmicro-channel and a first well, and the first micro-channel and thefirst well are both in the first substrate.
 2. The method of claim 1,wherein the delivery channel comprises a groove formed on a surface ofthe second substrate.
 3. The method of claim 1, wherein the deliverychannel comprises a groove formed on a surface of the first substrate.4. The method of claim 1, wherein the well has a inlet for receivingfluid, the micro-channel has an outlet for delivering fluid, and across-sectional area of the well inlet is greater than a cross-sectionalarea of the micro-channel outlet.
 5. The method of claim 4, wherein thecross sectional area of the well inlet is between one and twenty squaremillimeters, and the cross sectional area of the micro-channel outlet isbetween 100 and 10,000 square microns.
 6. The method of claim 4, furthercomprising forming a hydrophobic surface surrounding the micro-channeloutlet.
 7. The method of claim 1, wherein a second micro-channel and asecond well are in the first substrate, and the distance between thefirst and second wells is greater than the distance between the firstand second micro-channels.
 8. The method of claim 1, wherein the firstsubstrate has a thickness of at most 500 microns.
 9. The method of claim1, wherein the first substrate is bonded to the second substrate byspin-on bonding or high temperature bonding.
 10. A fluid deliverysystem, comprising: a first substrate having a micro-channel and a wellboth formed through the first substrate; a second substrate on the firstsubstrate; and a delivery channel formed between the first and secondsubstrates, wherein the delivery channel provides fluid communicationbetween the micro-channel and the well.
 11. The system of claim 10,wherein the delivery channel comprises a groove formed on a surface ofthe second substrate.
 12. The system of claim 10, wherein the well has ainlet for receiving fluid, the micro-channel has an outlet fordelivering fluid, and a cross-sectional area of the well inlet isgreater than a cross sectional area of the micro-channel outlet.
 13. Thesystem of claim 12, wherein the cross sectional area of the well inletis between one and twenty square millimeters, and the cross sectionalarea of the micro-channel outlet is between ten and 10,000 squaremicrons.
 14. The system of claim 12, further comprising a hydrophobicsurface surrounding the well outlet.
 15. The system of claim 12, whereinthe micro-channel extends both above and below a surface of the firstsubstrate.
 16. The system of claim 12, wherein the first substratecomprises a plurality of substrates.
 17. The system of claim 10, furthercomprising a probe for receiving fluid from the micro-channel, whereinthe micro-channel has an outlet for delivering fluid to the probe, andwherein the probe is moveable to and from the micro-channel outlet. 18.The system of claim 10, further comprising a third substrate on thesecond substrate.
 19. The system of claim 10, wherein the secondsubstrate has first and second extended channels both formed through thesecond substrate, a second delivery channel is formed between thesecondhand third substrates, the first extended channel is in fluidcommunication with the micro-channel and the second extended channel isin fluid communication with the well, and the second delivery channelprovides fluid communication between the micro-channel and the well. 20.A method for forming a micro-pipette, comprising: etching a top surfaceof a substrate to remove a portion of the substrate, wherein thesubstrate has a micro-channel formed through the first substrate, thetop surface is opposed to a bottom surface, and the top surface, thebottom surface, and the micro-channel, are coated with a supportmaterial.
 21. The method of claim 20, wherein the micro-channel isformed using reactive ion etching.
 22. The method of claim 20, whereinthe forming of the micro-channel comprises performing a first etch onthe top surface and a second etch on the bottom surface.
 23. The methodof claim 22, wherein the first etch forms a first channel having a firstwidth and the second etch forms a second channel having a second width,and the first channel is in fluid communication with the second channel.24. The method of claim 20, wherein the coating of the top surface, thebottom surface, and the wall comprises growing a layer of oxide on thesubstrate.
 25. The method of claim 20, wherein the support materialcomprises a dielectric.
 26. An apparatus for transferring fluid,comprising: a substrate having a top surface opposed to a bottomsurface; and a layer of support material, wherein the substrate and thelayer of support material form a micro-channel, the micro-channel opensat the bottom surface of the substrate and extends above the top surfaceof the substrate.
 27. The apparatus of claim 26, wherein the thicknessof the layer of support material is less than half the thickness of thesubstrate.
 28. The apparatus of claim 26, wherein the micro-channelforms an inlet at the bottom surface and an outlet opposed to the inlet,wherein the cross-sectional area of the outlet is less than thecross-sectional area of the inlet.
 29. The apparatus of claim 28,wherein the ratio of the cross-sectional area of the outlet to thecross-sectional area of the inlet is between 1 to 1 and 1 to 10
 30. Theapparatus of claim 26, wherein the thickness of the layer of supportmaterial is between one and ten microns.
 31. A micro-pipette, formed bythe method of claim
 20. 32. A method of forming a biological array,comprising: applying a plurality of fluids to a plurality of probes fromthe fluid delivery system of claim 10; and applying the plurality offluids onto a substrate from the plurality of probes; wherein each fluidcomprises a biological compound.
 33. The method of claim 32, wherein thebiological compound is a nucleotide.
 34. The method of claim 32, whereinthe biological compound is a protein.